Heat shields, which have to withstand hot gases of 1000 to 1600 degrees Celsius, are used in many technical applications. Particularly gas turbines, as are used in power-generating power stations and in aircraft engines, have correspondingly large surfaces inside the combustion chambers which have to be shielded by means of heat shields. Owing to the thermal expansion and owing to large dimensions, the heat shield is assembled from a large number of individual, generally ceramic, heat shield tiles which are fastened on a support structure, and neighboring tiles are spaced apart with a sufficient gap.
This gap provides the heat shield elements with sufficient room for thermal expansion. Since, however, the gap also enables direct contact of the hot combustion gases with the metal support structure and the retaining elements of the heat shield tiles, cooling air is injected through the gaps in the direction of the combustion chamber as a countermeasure.
A generic-type heat shield therefore comprises a support structure and a number of heat shield tiles which are detachably fastened on the support structure by means of retaining elements, wherein each heat shield tile has a cold side facing the support structure and a hot side which lies opposite the cold side and can be acted upon by a hot medium. For protection against hot gases, at least one cooling air passage is provided in the support structure.
The generic-type retaining element has a fastening section which is fastened on the support structure and a retaining section with a retaining head which is configured for engaging in an engagement device provided on the heat shield tile. With the fastening section fastened on the support structure and the retaining section engaging the heat shield tile, the fastening section has an upper side which faces a cold side of the heat shield tile.
EP 1 701 095 A1 discloses a heat shield, referred to in the introduction, of a combustion chamber of a gas turbine with a support structure and a number of heat shield tiles which are detachably arranged on the support structure. For protection of the combustion chamber wall, the heat shield tiles are arranged in an extensively covering manner on the support structure, leaving expansion gaps, wherein each heat shield tile has a cold side facing the support structure and a hot side which lies opposite the cold side and can be acted upon by a hot medium. The heat shield tiles are fastened on the support structure in a sprung manner by means of two metal retaining elements in each case. To this end, each retaining element comprises a retaining section, with an engagement section, and a fastening section. Retaining grooves are introduced into each heat shield tile on two opposite circumferential sides so that for retention of the heat shield tile the engagement sections of the retaining elements can oppositely engage in the retaining grooves. The retaining elements which are oppositely fastened on the heat shield tile in this way are guided by their fastening section in a fastening groove, extending beneath the heat shield tile, in the support structure. For protection against hot gases, the engagement sections of the metal tile holders are cooled. To this end, openings are introduced into the tile holders in the region of the retaining section and into the retaining latch of the heat shield tiles, which openings align with a cooling air hole which is arranged in the support structure so that cooling air from the cooling air hole, flowing in a direct line, impinges upon a cold side of the engagement section.
Despite this cooling of the engagement sections according to the prior art, with hot gas acting upon the heat shield, entry of hot gas in the region of the expansion gaps between the heat shield tiles can occur. The hot gas can then spread beneath the heat shield tiles and lead to scaling of the support structure.